Photometric analysis of liquids typically uses two photometric cells (or cuvettes) or one photometric cuvette. When two matched cuvettes are used, a first cuvette with sample is used as a blank to zero the photometric instrument, and then an optical value for an analyte of interest is obtained using a matched cuvette with sample to which analytical agents have been added. It is recognized that nicks and scratches from handling may cause an optical mismatch between cuvettes and introduce error into the test results. Accordingly, it is customary to discard matched cuvettes that have been nicked or scratched.
When one cuvette is used, the cuvette with sample is inserted into the photometric instrument as a blank to zero the instrument, and after zeroing the instrument and removing the cuvette, analytical agents are added to the sample, and then the cuvette is re-inserted into the instrument to obtain an optical value for an analyte of interest. It is recognized that because cuvette orientation in a photometric instrument will greatly affect test results, a cuvette should always be inserted into the instrument so that the cuvette has the same orientation to the light path, and that variability in the geometry and quality of the glassware can cause variability in results.
Furthermore, it is recognized regardless whether one or two cuvettes are used, that a cuvette exterior should be free of smudges or fingerprints or water droplets to ensure accurate readings. Useful photometric instruments include filter photometers, photometers without filters, and spectrophotometers, and typically provide an optical path length of 1 cm or longer. Photometric analysis of liquids includes colorimetric analysis and turbidimetric analysis. By “turbidimetric analysis” is meant, for purposes of this description, analysis based upon measuring the effect of fine suspended particles on a light beam.
As illustrated by U.S. Pat. No. 4,353,869 to Guth, it has been described to photometrically test for intoxication by inserting an end of a bubbler tube into an analytical agent-containing liquid contained in a glass ampoule, by then inserting the resulting assembly into a photooptical apparatus, by then nulling the photooptical apparatus, and by then bubbling deep lung breath from a suspect through the end of the bubbler tube into the liquid and taking a photometric reading. A mixing action is provided by the deep lung air bubbling through the analytical agent-containing liquid.
A pH/conductivity, water resistant meter that includes a conductivity cell with built-in electrodes and a pH sensor well, is commercially available from Myron L Company of Carlsbad, Calif. The pH sensor includes a protective cap. The meter is not useful for photometric analysis.
Also described in the prior art, as illustrated by U.S. Pat. No. 3,937,613 to Rosicky and U.S. Pat. No. 4,275,031 to Fischer et al, are reagent delivery devices that include a support such as an inert plastic strip or the like, and that release certain analytical agents into a sample for calorimetric evaluation of sample color. The sufficiently rigid supports of such devices may be used to stir the sample. Fisher et al teach the use of certain embedding polymers that dissolve in water to release analytical agents and form an optically clear solution, and disclose a broad range of embedding polymers, analytical agents, and analyses.
As can be recognized from the foregoing description of photometric analysis prior art, there continues to be a need for improved photometric analysis of liquids. It would be beneficial to minimize manipulations, reduce the time and labor required for analysis, and to reduce variability of measurements. It would be beneficial is to avoid the need for matched cuvettes, and to avoid any concern about the use of cuvettes with nicks or scratches.